The present invention relates generally to a new semiconductor process, and more particularly, to a new semiconductor process in which a plating enhancement layer is utilized to facilitate the plating of copper.
Semiconductor device interconnection technology has made giant advancements to meet the requirements of increased device density and circuit performance. To meet the ever increasing device density demand, a double damascene method for interconnecting the semiconductor devices is widely utilized. Among other attributes of double damascene methodology, it allows the definition of a complex pattern of interconnection lines and via-studs with essentially no restriction on the number of layers of materials used in the interconnections. This feature of damascene methodology allowed the introduction of copper metallurgy which requires a variety of barrier layers and different metal deposition methods. In order to meet the improved circuit performance by reducing the parasitic impedance losses, it was soon found that a low dielectric constant (i.e., low k) dielectric material is desirable to complement the increased conductivity offered by copper metallurgy. Accordingly, low k dielectric material and copper metallurgy interconnection defined by dual damascene methodology is the present day choice for interconnections in high performance semiconductor device processing.
Electrochemical deposition of copper has been found to provide the most cost-effective manner in which to deposit a copper metallization layer. In addition to being economically viable, such a deposition technique provides substantially conformal copper films that are mechanically and electrically suitable for interconnect structures. Electrochemical deposition of copper, however, is generally only suitable for applying copper to an electrically conductive layer. As such, an underlying conductive seed layer, typically copper, is generally applied to the workpiece before it is subject to the electrochemical deposition process.
The copper seed layer is typically deposited by a physical vapor deposition (PVD) process or a variant thereof such as an ionized PVD (IPVD) process which results in non-conformal deposition which has heretofore worked well. However, as critical dimensions get smaller, for example less than 45 nm, the seed layer may pinch off the damascene openings, thereby leading to incomplete coverage and voids. To avoid this problem, the copper seed layer may be thinned or alternative seed layers such as ruthenium may be utilized. Either of these changes result in increased resistance of the metal stack, hence requiring plating tool modifications for uniform plating across the wafer without which the center of the wafer would plate substantially thinner than the edge of the wafer.
A new methodology is needed to assure uniform plating of a copper damascene interconnect structure. The present invention contemplates the use of an optically transparent and conductive plating enhancement layer such as tin oxide or indium oxide which would also serve as an etch hard mask.
The use of conductive oxides for different applications has been proposed. For example, French et al. U.S. Pat. No. 6,885,425 discloses a method of making a liquid crystal display. According to the foregoing patent, a silicon nitride layer is formed then a layer of indium tin oxide is deposited over the silicon nitride. Thereafter, the indium tin oxide is patterned to form openings and palladium followed by copper or silver is selectively deposited on the indium tin oxide and adjacent to the openings in the indium tin oxide. Others have proposed similar applications. Thus, Koh et al. U.S. Pat. No. 6,787,441 have proposed indium oxide or indium tin oxide for the electrode of semiconductors or a liquid crystal display, Mason U.S. Pat. No. 5,280,381 has proposed an electrochromic device comprising a metal oxide (e.g., tin oxide) on a support substrate, Ritchie et al. U.S. Pat. No. 4,977,013 have proposed a liquid crystal display comprising tin oxide or indium tin oxide on a polymeric substrate and Basol et al. have proposed photovoltaic devices in which there are semiconductor layers on a transparent electrically conductive layer such as indium tin oxide or tin oxide. The disclosures of all of the foregoing patents are incorporated by reference herein.
However, none of the foregoing references pertain to the uniform plating of copper damascene interconnects.
Accordingly, it is a purpose of the present invention to have a new methodology to assure uniform plating of copper damascene interconnects across the wafer.
It is another purpose of the present invention to have a plating enhancement layer that is effective in assuring uniform plating of a copper damascene interconnect structure.
These and other purposes of the invention will become more apparent after referring to the following description of the invention in conjunction with the accompanying drawings.